Sidebery - Manage your tabs and bookmarks in sidebar.
Simple Tab Groups - Create, modify and quick change tab groups. Features:
Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.
Firefox Multi-account Containers - Sign in to two different accounts on the same site
Panorama View - Tab Groups with Panorama View. Lets you easily Group and manage Tabs visually, with tab hiding.
Tab Workspaces - Organize your tabs into workspaces.